I'm not trying to question your abilities or knowledge, but it may be something before the ignition...

We had a similar situation on a tandem once. Big V-549 would light instantly, run like a dream, and then once out on the road and warm would begin to run like a sh*&house, and then quit. Leave it there for a while, and it would light again. It was an electronic ignition, (no points etc.) but we looked over many ignition components until we discovered the culprit - key switch.

Seems after a while, the switch would start to get warm, voltage would drop to the ignition... etc. Shut the truck off - i.e. key switch wasn't carrying current, ergo it cooled, and 20 minutes later (or less) it would light up ready for action (motor and engine compartment would still be quite warm)...

So, perhaps it would be worthwhile to check your supply votage to your ignition by turning the key on, and simply seeing if your voltage drops as the electrical system warms up. It might be the switch itself, or a voltage drop across a relay somewhere that compounds the problem by dropping voltage = more current = more heat = more voltage drop..... and on and on.

It might not pertain to you, today, but someone else reading this might recognize the symptoms...

Luke   aka Ken